1. Field of the Invention
The present invention relates to an electrode for a dielectric thin film device which has a superior crystalline characteristic, a method of manufacturing device, and an ultrasonic wave oscillator using it. More particularly, the present invention relates to an electrode for a dielectric thin film device which comprises a diffusion preventing layer suppressing diffusion of unnecessary elements into an uppermost surface layer of a underlying electrode, which causes deterioration of the dielectric thin film characteristics, a method of manufacturing device, and an ultrasonic wave oscillator using the electrode.
2. Description of the Prior Art
Dielectric substances mean materials having a variety of characteristics such as paraelectric, ferroelectric, pyroelectric, and piezoelectric properties. The devices to which these dielectric thin films are applied are being employed in extensive fields. Many of the devices in which a dielectric thin film is used require at least the dielectric thin film and an electrode for driving the film. Formation of the dielectric thin film is performed by a variety of thin film forming methods such as a sputtering or a chemical vapor deposition (CVD). In such methods, except when only a few materials such as zinc oxide or aluminum nitride are used, the formation is often carried out at a high temperature in a range of 400.degree. C. to 700.degree. C.
This kind of tendency is found more frequently when a complicated chemical compound such as double oxide is made into a thin film rather than when a simple chemical compound is made into the one. The tendency is also found frequently when trying to manufacture a material of a high quality. When the driving electrode is formed after the formation of the dielectric thin film, the material is determined mainly by electrical characteristics required, and no other major restriction is needed.
However, when, in view of the device configuration, the driving electrode can not help being formed before a process in which the dielectric thin film is formed, many problems occurs. The most difficult problem is as follows: At the time of the dielectric thin film formation, in some cases, the electrode may suffer from a thermal deterioration such as the oxidation in the environment, and the electrode may react with the dielectric thin film, thus causing a deterioration of the characteristics in the two. In order to avoid such phenomena, a noble metal such as platinum is so often employed generally as a material for the electrode.
Also, only the platinum does not necessarily brings about an enough adhesive property for a ground on which the electrode is formed, for example, a silicon oxide film, and thus there exists a possibility that defects such as the peeling take place. Accordingly, in most cases, a substance such as metal titanium or metal chromium is formed between platinum and a substance such as silicon dioxide as an adhesive layer.
Chian-ping Ye et al. showed, in "Experimental studies on primary and secondary pyroelectric effects in Pb (ZrxTi (1-x)) O3, PbTiO3, and ZnO thin films" described in J. Appl. Phys. 1991, No. 70, p. 5538, a high sensitive pyroelectric sensor having a cavity of lifting structure to which applied is the dielectric substance (pyroelectric substance) in the title using microetching technology. Employed as an electrode in the pyroelectric sensor is an electrode configured by platinum and titanium.
Moreover, disclosed in JP-A No. Hei 6-350154 is a piezoelectric device of floating structure, which is formed by forming on a substrate an insulating film, a lower side thin film electrode, a piezoelectric film, and an upper side thin film electrode, and by then eliminating a substrate on the rear side of the substrate and a substrate under a portion which is to become a resonator. Employed in the device, too, is an electrode configured by platinum Pt and titanium Ti.
As described above, in many cases, the electrodes, which are constituted by a combination of a noble metal represented by platinum and a metal of a superior adhesive property represented by titanium, are easy to be applied to a variety type of dielectric thin films and thus are so widely used.